This invention pertains to the art of pressurized fluid systems and more particularly to an apparatus for regulating the pressure in the system.
The invention is applicable to a pressure regulator and will be described with particular reference thereto. However, it will be appreciated that selected aspects of the invention may have application in related fluid environments and uses.
U.S. Pat. No. 5,033,505 discloses a predecessor pressure regulator, the disclosure of that patent being hereby incorporated by reference. The structure disclosed therein includes a pressure responsive member disposed in a hermetically sealed housing. The pressure responsive member includes a stationary portion fixed to the housing and a movable portion interconnected thereto by a flexible member, such as a bellows. The pressure responsive member has a predetermined pressure charge enclosed therein so that axial movement occurs varying the volume and pressure in response to fluid pressure in the housing.
A self-threading poppet assembly is secured to the movable portion of the pressure responsive member. Preferably, a poppet is disposed in an inlet fluid line and cooperates with a valve seat defined at the interconnection of the inlet fluid line and the housing. The poppet is comprised of a suitable seal material that is preferably tapped upon threaded engagement with a poppet stem. This arrangement provides for a controlled, precise opening between the poppet and valve seat so that desired operational characteristics of the regulator can be achieved in accordance with design parameters.
As disclosed in the '505 patent, the poppet assembly is secured to the pressure responsive member by means of a stem clip. The stem clip includes a series of bent portions for reasons set forth in the patent. Although adequately addressing particular needs of the industry, it has been deemed desirable to provide an alternative arrangement that is less expensive to manufacture and satisfies other criteria. For example, the detailed bending in the prior arrangement consequentially raises the cost of manufacture of the stem clip. Unfortunately, the bent configuration of the clip also does not lend itself to providing a highly polished surface finish. Since certain fluid systems using these types of regulators have stringent cleanliness standards, the surface finish of each component of the regulator can be very critical.
As also detailed in the '505 patent, at high flow rates, known pressure regulators have a tendency to oscillate. In fact, the oscillations occasionally result in an audible buzzing, and the oscillations can result in pressure variations in the fluid system downstream of the regulator. That patent proposes use of a dampening means, such as an O-ring, interposed between the movable and stationary portions of the pressure responsive member. The dampening means exerts a slight drag on the axial movement of the movable portion which has proved to be highly effective in addressing the oscillation problem encountered at high flow rates.
A potential drawback to this arrangement is the effect of the dampening means on low flow rates. Specifically, the friction between the O-ring and an associated surface can limit the sensitivity of the pressure responsive member at low flow rates. Potentially, minute changes in pressure will not be effectively addressed by a pressure responsive member that incorporates a dampening means intended to resolve oscillation problems associated with high flow rates. Accordingly, it has been deemed desirable to maintain the oscillation dampening features at high flow rates, as well as to address concerns with sensitivity at low flow rates.
Still another benefit of the '505 patent is the provision for moving the pressure responsive member to a closed position if the charge is lost. For example, if the bellows were to leak and release the pressure charge, the poppet would seal against the valve seat and isolate downstream equipment from high pressure. The construction of the bellows tends to flatten under such conditions so that the pressure responsive member, particularly the poppet, moves to a shut-off or closed position with the valve seat. Due to the imprecise nature of the bellows construction, though, it has been deemed desirable to provide a positive action to urge the poppet to a closed position if the bellows loses its internal charge.